The present invention relates to drywall corner beads, particularly drywall corner beads having an outer paper layer, and paper therefor.
Current building construction techniques frequently call for the use of drywall sheets, otherwise called wallboard, to form the surfaces of interior walls. Sheets of drywall are made by encasing sheets of plaster with heavy construction paper. The paper provides extra strength and resistance to tearing and prevents crumbling of the enclosed plaster. The sheets of drywall are typically produced in sizes of four feet by eight feet to four feet by twelve feet. These sheets can be installed intact or can be cut to custom fit specific interior wall sizes. When cut, the inner plaster is exposed and is particularly vulnerable to crumbling or other damage unless the severed edges can be protected. An exposed corner, exterior or interior, formed by two interfacing drywall sheets not in the same plane is also susceptible to damage. Damage can be particularly severe when these corners involve cut or exposed edges. To overcome this vulnerability to injury and further reinforce the exposed corner formed by two interfacing drywall sheets, a drywall corner bead will generally be installed at that corner. The corner being reinforced can be either an interior or exterior corner.
Two types of drywall corner beads are typically used in reinforcing drywall corners, a paper faced bead or paperbead type, and a non-paper faced bead or all-metal drywall trims. Both the paperbead type and the all-metal drywall trims typically include a strip of metal formed or extruded into a desired shape, although molded plastic can also be used. One common example involves forming the metal strip into a core shape having two flanges and a center rib positioned between them. This form of corner bead is called a rib-type of corner bead. Another common type of corner bead has two flanges and a larger curved portion or bullnose positioned between them. This type of corner bead is called a bullnose corner bead. A third type of corner bead is an L-shaped type having one flange longer than the other and an offset rib between the flanges. Other types of corner beads include a J-shaped type, a splay-bead type, and a shadow-mold type.
All-metal drywall trims are attached to drywall by driving nails, screws, staples or other fasteners through the flanges, securing the drywall trim with the heads of the fasteners. A joint compound is then applied to cover the flanges and fastener heads. The compound is sanded and feathered to provide a smooth and continuous surface from the drywall surface to the center rib of the formed metal strip.
Paperbeads provide several advantages over all-metal drywall trims. For instance, both paint and joint compound adhere significantly better to the surface of a paperbead than to the exposed metal surface of a typical nail-on corner bead. Moreover, paint applied directly to a metal surface is easily chipped after drying. Drywall corners covered with nail-on corner beads are also more susceptible to cracking along the edges of the flanges. Thus, a paperbead provides a better surface for paint adhesion and helps reduce plaster cracking.
Paperbeads differ from all-metal drywall trims in several respects. First, the paperbead has a paper strip attached to an outer surface of the formed metal or plastic core previously discussed. Generally, portions of the paper strip extend beyond the edges of the metal or plastic core forming wings. The paperbead is attached to drywall corners by applying a joint compound to the drywall surface and embedding the formed metal strip and the paper wings in the compound; or it can be nailed on and then compound is applied. A second, exterior layer of joint compound is subsequently applied on top of the paperbead and allowed to dry. This exterior layer of joint compound is then sanded and feathered to form a smooth and continuous surface between the drywall and the corner bead. The steps of applying, sanding and feathering the exterior layer of joint compound can be repeated until a smooth surface is created. Throughout this process, the portion of the paper strip covering the corner bead, i.e. the center rib, the bullnose, or the offset rib, is left exposed or uncovered by joint compound.
The paper surface left exposed on a typical paperbead may be scuffed, or completely removed during the sanding and feathering process, thus exposing the metal surface beneath. Scuffing makes it more difficult to later obtain a smooth painted surface at the corner bead because the paper becomes frayed or fuzzy. Also, as stated previously, paint does not adhere as easily to the exposed metal surfaces. Therefore, paint applied to any exposed metal surface will be more easily chipped after it dries. Moreover, a scuff in the paper surface produces a break in the line of the corner bead and reduces the aesthetic benefits of having such a bead.
Joint tape made from paper strips is also used to cover the joint between two abutting sheets of drywall. The joint tape is applied to a thin layer of joint compound covering the joint, covered with an exterior layer of joint compound and sanded and feathered to form a smooth and continuous surface. As with corner beads, the joint tape can be subjected to abrasive contact that can scuff and tear the joint tape, making it difficult to obtain a smooth surface for painting.
To overcome the problems of scuffing, some paperbeads provide a surface coating at the exposed center portion of the corner bead to improve the paper's resistance to abrasion and avoid the problems caused by scuffing. This type of surface coated paperbead is disclosed in U.S. Pat. No. 5,131,198. A surface coating, however, only provides extra resistance to abrasion at the outer surface of the paper strip. If this coating is penetrated or removed by the sanding process, the underlying paper is exposed and is again made susceptible to scuffing. Consequently, the problems of paint adhesion, unsmooth surface finishes and paint chipping are not avoided. Moreover, the application of a surface coating at a particular location involves an additional manufacturing step thereby increasing the cost of making the product.
To resolve the problem of surface coated paper, U.S. Pat. Nos. 5,836,122 and 5,613,335, both to Rennich et al., propose a paperbead for protecting drywall corners containing a paper strip bonded to a metal or plastic core throughout its thickness. This paper strip is made of stack paper which is uniformly impregnated with latex which imparts scuffing and abrasion resistance to the paper.